Diff of two XML's using XSLT

This may be commonly solved problem but I yet to see it discussed
anywhere and search has not shown up anything..

Say, for example, you generate some "clean" XML using TIDY and then
you want to compare the before and after using something like WinDiff
etc.

Instead I would like to know if someone has written and XSLT template
that can compare two XML files and "diff" them, producing perhaps HTML
output showing missing on either side and differences?

Thanks!
Guy